The present application relates to duct assembly, and more particularly, to a fire-rated modular duct assembly suitable for exhausting flammable or hazardous gases, vapour and the like.
Many processes in commercial and industrial facilities generate flammable or hazardous gases, vapors or particles. The hazardous material must be captured at the source and transported or moved through the facility (e.g. building) to a location where the material can be discharged, e.g. directly into the atmosphere, or into a collection or a treatment system within the building or exterior to the building.
In a typical facility, ventilation ducts are routed throughout the building. The ventilation ducts penetrate and cross fire separations, and typically comprise interior dampers installed within the fire separation section to prevent fire that penetrates the duct from travelling through the duct across the fire separators in the building. It will be appreciated that while such an implementation may be sufficient for the fire protection of ventilation ducts, ventilation or exhaust ducts for flammable or hazardous materials cannot be configured with fire dampers, so the duct itself must be fire-rated.
To be classified as a fire-rated duct, an exhaust duct must be capable of preventing the release of flammable materials from inside the duct and/or combustible materials adjacent the exterior of the exhaust duct from catching fire if a fire exists on the other side of the duct. In other words, a fire-rated duct must be capable of minimizing the transfer of heat through or across the duct walls. It is also desirable to maintain the wall thickness to a workable minimum.
Fire-rated ducts are typically found in installations such as commercial kitchens and laboratories.
In a commercial kitchen, the exhaust hoods are configured to capture grease laden air over deep fryers and grills, which is extremely flammable, and must be transported through the building to an exterior area where it can be safely discharged. Due to the flammable nature of the exhausted vapour, a minor fire, for example, in the kitchen could enter the exhaust duct and quickly spread throughout the duct system. As a result, any potential fire inside the duct system must be contained and thermal transfer through the duct walls limited to prevent ignition of adjacent combustible material in the kitchen or other areas of the building. In addition, the exhaust duct system must be capable of preventing the ignition of the grease laden air from a fire source in another part of the building and then spreading to the kitchen or other parts of the building where the exhaust duct system is routed.
In a laboratory installation, the exhaust system is configured to collect and exhaust chemical vapours, including vapours from chemicals with low flash points, and contain any fire inside the duct system, or prevent an external fire from igniting the vapour inside the duct system.
Known fire-rated exhaust duct systems are typically fabricated in sections, and the section are shipped to the installation location. At the installation location, the sections are welded together to form continuous conduits or conduit sections. Due to field conditions, the welding could be of poor work quality due to limited space and/or setup. This meant expensive rework and re-welding to seal leaks in the duct system during pressure testing. Conventional fire-rated duct systems typically required the installation of an additional gypsum fire-rated enclosure (approximately 10″ thick) around the duct. In addition to requiring an additional step, the gypsum enclosure was typically constructed/installed by another trade.
In an attempt to overcome the known shortcomings in the art, chimney manufacturers introduced pre-fabricated fire-rated exhaust ducts based on a modification of existing chimney exhaust systems. While these pre-fabricated fire-rated exhaust ducts addressed shortcomings of existing systems, the characteristic round profile significantly limits the volume of air that can be vertically carried in conventional building footprints, and in a horizontal configuration, the round profile or cross section is often too large to fit into conventional ceiling space spaces or dimensions.
Accordingly, there remains a need for improvements in the art.